Polyhydroxyalkanoate(PHA)is a typical degradable biopolymer,which has biodegradability and biocompatibility compared with traditional plastics.Using it to replace traditional plastics can minimize carbon dioxide emissions and reduce the accumulation of plastics in the natural environment,thereby reducing environmental pollution.Due to the high cost of raw materials and the high operating costs,it is difficult to scale the application.Both free nitrous acid(FNA)and alkyl polyglucose(APG)have the ability to promote the dissolution and hydrolysis of sludge.Using FNA pretreatment combined with APG to treat the excess sludge can enhance the voliate fatty acids(VFAs)yield of sludge.At present,using mixed microorganisms of activated sludge to synthesize PHA with VFAs-rich fermentation liquid from sludge as a substrate has become a hot spot in the field of biosynthesis.The method can not only effectively treat and utilize the sludge,but also reduce the cost of PHA synthesis,which has certain economic and environmental benefits.In this paper,based on the VFAs composition of the fermentation liquid under the optimal acid production conditions for FNA pretreatment combined with APG treatment of excess sludge.Two SBRs inoculated with two different sludges to enrich PHA-producing microorganism were started to study the PHA synthesis effect of mixed microorganisms using simulative fermentation liquid as the substrate.The effect of p H,C/N and C/P on the PHA synthesis was investigated in batch experiments.The PHA synthesis effect with the actual fermentation liquid from sludge as the substrate was studied.Using the simulative fermentation liquid as the substrate to start two SBRs with different sludge.SBR#1 was inoculated with sludge from the secondary settling tank of the Waste Water Treatment Plant(WWTP),and SBR#2 was inoculated with the mature PHA-producing mixed microorganisms that was cultivated with glucose as the substrate.Studying the changes of the operation stability parameters,PHA synthesis index parameters and kinetic parameters involved in the enrichment process,the results showed that the sludge concentration of the two reactors tends to be stable with the passage of enrichment time,and SBR#2 has stronger PHA synthesis ability to obtain higher PHA yield.However,with the passage of enrichment process,the performance of SBR#1 is better,which obtain the maximum PHA yield(12.54wt%)of enrichment process and the cumulative PHA yield(51.66wt%)in batch test at117 days.Using high-throughput sequencing technology to analyze the structural characteristics of mixed microorganisms during the enrichment process.With the passage of enrichment time,the relative abundance and biodiversity of the microbial community in the reaction system showed a downward trend.The relative abundance of the dominant genus Meganema in the reaction system is increased,therefore the PHA synthesis performance of the mixed microorganisms is the best;and the relative abundance of Meganema in SBR#1 is higher than that of SBR#2,resulting in SBR#1 also has better PHA-producing ability than SBR #2.The effect of p H,C/P and C/N on the synthesis effect of PHA in the batch test was investigated.The results showed that: the influence of the phosphorus limitation process on the PHV synthesis is greater than that of PHB in the batch optimization experiment.The optimal conditions for the PHA synthesis process are p H of 8,C:P of 100:0.03,C:N of 125:1.Under this condition,the cumulative PHA content is 57.34wt% and the specific synthesis rate of PHA is 1.4855 mg COD/mg X/h.In order to further explore the problems that may be encountered in the actual application of PHA synthesis by the fermentation liquid,using the actual fermentation liquid obtained by FNA pretreatment combined with APG treatment of the excess sludge as the substrate for the synthesis of PHA.The results showed that the optimal reaction conditions for removing nitrogen and phosphorus in fermentation broth by struvite precipitation method were: T of25℃,p H of 11.0,Mg/P molar ratio of 2.6/1,and reaction time of 10 min.Under this condition,the removal rate of phosphorus and ammonia nitrogen reached 97.94% and 35.10%,respectively.The cumulative PHA content synthesized with the actual fermentation liquid was 24.43wt%,and the final content of PHB and PHV were 16.62wt% and 7.82wt%,respectively. |